Concentrate
by Kegler

Eight Across entries squeeze two letters into one square.  In each instance, the intersecting Down entry squeezes two different letters into the same square.  The unclued entry at 23A describes the result.

Across 1 Competition in foreign market, etc. (2 wds) 7 Child of Eve placed with husband 11 Eccentric pro had scorn for Moors (2 wds) 12 Martin Luther has a couple of issues with Southern bussing 14 Gentle retriever returns, belonging to me 16 One pushing, ultimately, one line Kegler left out 17 Back even, winning a thousand, quit 18 Like a judge's swirling robes? 21 I'd sent back Stallone's poetry 22 Stories name actress Sophia 23 See instructions 26 Periodically without much force, we hear 27 Tree contains trace of extraordinary indigo varnish ingredient 30 Carol catches ending of “Get Smart” 31 Prohibit stocking red grain product 32 Vaccine inventor crosses unusually wide pedestrian pathway 37 Two northeastern states rejected Arab leader 38 Heartless spy bribes computer network honchos 39 Flavoring agent from small fruit; 30 seconds work? (2 wds) 40 Hovel welcomes a visit 41 Yes, Tim, a test includes guesswork

Down 1 Smear I covered with powder, per Jewish tradition 2 Took a break in grass surrounding street 3 Children primarily tease pony 4 Incomplete list includes individual's cat 5 Italian family tees off 6 Raising wrong net, train with club for indoor sport (2 wds) 7 Rolls up with disdain 8 Relax - what's wrong? 9 That woman hugging Roger is initially more mawkishly sentimental 10 Doctor Wye bringing back half of nurses for test (2 wds) 13 Blackbird eating fancy donut in ship's mooring equipment (2 wds) 14 Debut of stocks contributed to boom and bust 15 Ken Lay's distributed certain hydrocarbons 19 Fish interest some singers 20 Thorny bushes restricted within stiff supporters? 24 Having less chance of a favorable outcome, physician admits ill mime 25 Cattle relative's undirected motion 26 Most learned among brothers-in-law is esteemed 27 Yokel excitedly describing start of game with green and yellow ball? (2 wds) 28 “Leg twisted at gym,” claims one flyer 29 Mischief-makers going after women and weaklings 33 Stop; time for food 34 Leery of war club 35 Appearances of one in certain clothing department 36 Lots of land in the outskirts of Ames, Iowa

Solution