The unclued lights (one of two words, one of three and-another of four components) are of a kind. Chambers gives only a cognate of the solution at 7 Down.

Across

9    River in middle of West Bank city (4)
11    Seafarer of marked individuality, but primitive (10)
12    Clear illustration includes appendage of seed (4)
16    Poem put in order, apart from opening lines (5)
17    Assault the centre of town in County Durham (5)
20    Steering clear of 4, except on the way back (7)
21    Disturb queen, in peril after loss of rook (7)
23    Mercian rioted in peninsular war (7)
24    Duet composed before English solo (5)
25   ...