Solution to 20A has been deliberately left unsolved and is to be answered only by a non-regular / novice commenter, with proper annotation. Those who have answered earlier in the week, please give others a chance.
Open for anyone to answer, if not solved by 1 PM.
ACROSS
1 Understated caption - it's released (6) SUBTLE SUBTitLE
4 Small vehicle going around Hollywood that lacks direction (6) SCALAR {S}{CA{LA}R} Hollwood is in LA but that cannot mean Hollywood is LA
8 Value of ammos? Double, often at America (7) MODULUS {aMmOs+DoUbLe}{US}
9 Send Tom batting last (7) ENDMOST*
11 Random ancient philosopher drinks & drinks...mainly tequila (10) STOCHASTIC {STO{CHA'S}{Te...a}IC}
12 Cut one's shaft (4) AXIS {AX}{1'S}
13 Meeting place for mostly getting drink (5) FORUM {FOr}{RUM}
14 After second act, musical drama's filled with power, a bit of sadness, and vitriol (8) COPPERAS {aCt}{OP{P}ERA}{Sa...s}
16 Precision of account office (8) ACCURACY {AC}{CURACY}
18 Problem of mass lacking time (5) ISSUE tISSUE
20 Radical's also returning to base (4) ?O?T (Addendum ROOT {R}{TOO<=} - See comments)
21 Unbroken fake money - dubious bid to run off (10) C ONTINUOUS {CON}{TIN}{dUbiOUS}
23 Mathematical operator kids essentially turn to cover (7) DIVISOR {kIDs<=}{VISOR}
24 Dynamic family name recalled (7) KINETIC {KIN}{CITE<=}
25 Husband part of surprisingly great group (6) GATHER {H} in {GREAT}*
DOWN
1 Discharge fourth slip after second wicket (5) SPOUT {sliP}<=>{S} and {OUT}
2 Ball - one can get you thrown out? (7) BOUNCER [DD]
3 Cancer of ileum and colon mainly - cadaver regularly needs to be dissected (9) LEUCAEMIA {ILUEM+Co..n+cAdAvEr}*
5 No introduction needed for legendary figure (5) CONIC iCONIC
6 Story about alcoholic drink and non-alcoholic drink (7) LIMEADE {LI{MEAD}E}
7 Suspend while turning it in saucer with tea, mainly while stirring (9) RUSTICATE {IT<=} in {SAUCER+Tea}*
10 Mail describing aunt's ultimate rotten and unpleasant death (6,3) STICKY END {S{aunT}{ICKY}END}
13 Mathematical operation to get information on gasket (9) FACTORING {FACT}{O RING}
15 Prudish one on TV- starting to expound about setter like a barbarian (9) PRIMITIVE {PRIM}{1}{T{I}V}{Ex...d}
17 Straighten out idiot following peacemaker by sticking a little sense in (7) UNTWIST {TWIT}<=>{UN} over {Se..e}
19 Boss and a specialist scholar (7) STUDENT {STUD}{ENT}
21 Selected carbon pipe (5) CHOSE {C}{HOSE}
22 Couple has free sex on the counter (5) UNITE UN(-ti+it}ITE
Reference List
Small = S, Power = P, Time = T, Radical = R, Husband = H, Second = S, Alcoholic drink = MEAD, Carbon = C, Sex = IT