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Hi all, and thanks to The Ace of Hearts for a satisfying solve.
The preamble:
From the answer to each clue a letter must be deleted wherever it appears before entry into the grid; definitions refer to the full unmutilated answer, wordplay and number in brackets, to the grid entry. In clue order, the omitted letters give a definition of a word in Chambers Dictionary which must be highlighted in the completed grid. The three unclued entries which might be called WEAPONS OF MASS DESTRUCTION are examples of this keyword. Chambers Dictionary (2016) is recommended.
I enjoy most wordplay gimmicks, but find this one of the harder types because the letters to be removed are not only missing from the wordplay but of course not present in the checkers. Still, it all came together slowly but steadily. As “war machine” and “boulders” came into view my first thought was (naturally) TREBUCHET. In fact, this particular weapon of mass destruction (nice play on words there) does not appear. The unclued entries revealed themselves to be SHANGHAI, ONAGER and BRICOLE, each a type of CATAPULT, the third definition of which in Chambers is:
(in ancient history) A WAR MACHINE FOR THROWING BOULDERS, ETC

| # | ANSWER | Clue with definition underlined | |
| Explanation, with quoted indicators in italics and ANSWER letters in bold caps | |||
| Across | |||
| 1a | VELLOZIA | Treelike plant’s length and weight measures taken in Virgin Islands (7) | A |
| ELL and OZ (length and weight measures) taken in VI (Virgin Islands) | |||
| 5a | MCEWAN | Aldershot-born novelist to strengthen sheltering civil engineer (5) | W |
| MAN (to strengthen) around (sheltering) CE (civil engineer) | |||
| 10a | WINONA | Secure Old Norse name for eldest daughter (5) | A |
| WIN (secure) + ON (Old Norse) | |||
| 11a | PEDALLER | Cyclist recalling group from Marbella depot (7) | R |
| The reversal of (recalling) part of (a group from) MarbELLA DEPot | |||
| 12a | EGHAM | Surrey town for example houses aborigines at first (4) | M |
| EG (for example) + Houses Aborigines at first | |||
| 14a | PRECAVA | Blood vessel before two thirds of local government (5) | A |
| PRE (before) + two thirds of loCal goVernment | |||
| 16a | BEECHEN | Antique wooden Frisbee Henry locks up (6) | C |
| FrisBEE HENry holds (locks up) the answer | |||
| 17a | BOXER SHORTS | Fighter picks out underwear (10, two words) | H |
| BOXER (fighter) + SORTS (picks out) | |||
| 19a | NUMERABILITY | Mineworkers try and bale out capacity to be quantified (10) | I |
| NUM (mineworkers) + TRY and BALE anagrammed (out) | |||
| 21a | INDICANT | Something that shows fool taking out oxygen for chief accountant (6) | N |
| IDI[o]T (fool) replacing O with (taking out oxygen for) CA (chief accountant) | |||
| 26a | ROTAPLANE | Type of aircraft roster to devise (8) | E |
| ROTA (roster) + PLAN (to devise) | |||
| 27a | FOR FEAR | Just in case injured are found in Oregon (5, two words) | F |
| An anagram of (injured) ARE found in OR (Oregon) | |||
| 28a | OXIME | Chemical compound to arrange by taking over from beginner (4) | O |
| tIME (to arrange), X (by) replacing the first letter (taking over from beginner) | |||
| 29a | LEINSTER | Open country housing institute in large area of Ireland (7) | R |
| LEE (open country) containing (housing) INST (institute) | |||
| 30a | TIEPIN | Ornamental dressing accessory stud that is at the front (5) | T |
| PIN (stud) with IE (that is) at the front | |||
| 31a | HERETO | Before answering to this (5) | H |
| ERE (before) + TO (answering) | |||
| 32a | HUCKSTER | Aggressive seller for all to see in zany sketch (7) | R |
| U (for all to see) in an anagram of (zany) SKETCH | |||
| Down | |||
| 1d | VOWESS | Clare perhaps sews very badly (5) | O |
| SEWS VERY anagrammed (badly) | |||
| 2d | WEIGH DOWN | Oppress cardinal endlessly, over river in Scotland (7, two words) | W |
| EIGHt (cardinal) without the last letter (endlessly) over DON (river in Scotland) | |||
| 3d | LINHAY | Local shed section of Lincoln Haymarket (5) | I |
| A section of LincoLN HAYmarket | |||
| 4d | INELABORATE | Simple aerial to be adjusted (10) | N |
| AERIAL TO BE anagrammed (adjusted) | |||
| 6d | CARPET BUG | Fish in France and almost shoot harmful insect in Paris (8, two words) | G |
| CARP (fish) + ET (in France, and) + almost BUd (shoot) | |||
| 7d | BELÉM | Brazilian port the Spanish remember in the centre (4) | B |
| EL (the Spanish) + remEMber in the centre | |||
| 8d | ALCOVE | Living without one to protect colt in shelter (5) | O |
| AL[i]VE (living) without I (one) surrounding (to protect) C (colt) | |||
| 9d | UNEVENLY | Oddly never undressed in front of Noel, on vacation in New York (7) | U |
| Without outer letters (… undressed) nEVEr in front of NoeL without inner letters (on vacation) all in NY (New York) | |||
| 13d | CHISEL TOOTH | Chose to hit broken squirrel’s fang say (10) | L |
| CHOSE TO HIT anagrammed (broken) | |||
| 15d | REDUCTANT | Liberal withdraws from resisting chemical substance (8) | D |
| L (Liberal) withdraws from RE[l]UCTANT (resisting) | |||
| 18d | OTTAMITE | With too much to confess, daughter abandoned Turkish citizen (7) | E |
| OTT (too much) + A[d]MIT (to confess), D (daughter) having left (abandoned) | |||
| 20d | APRAXIC | A short film tackling a variable of neurological disorder (6) | R |
| A and PIC (short film) going around (tackling) A and X (variable) | |||
| 22d | DORSER | Vagrant runs into agent (5) | S |
| R (runs) goes into DOER (agent) | |||
| 23d | ELLIPSE | Overturn elevated geometrical figure (5) | E |
| SPILL (overturn) rising (elevated) | |||
| 24d | ENTENTE | Hawaiian native follows English, understanding (5) | T |
| NENE (Hawaiian native) follows E (English) | |||
| 25d | DE-ICE | Use antifreeze on adhesive at regular intervals (4) | C |
| aDhEsIvE at regular intervals | |||
Thanks, Kitty for the fabulous blog. It’s like reading a short thriller.
Very short! But thanks for the comment, KVa. 🙂