Definitions in ten clues contain a misprint; corrections spell out a theme word. Unclued lights are four pairs of words of a kind, each relating to the theme word in a different way. Elsewhere, ignore one accent.
 

Across

11    Like some parasites? See ten in rotten tree house (12)
12    Statesman needs iron, regularly pale (5)
14    Flexible tenures for colony’s workers? (7)
16    Anglicans right, one’s sure to sin (4)
17    Libertine pockets good cosmetic (5)
22    Small horn’s whorl (8)
23    Climber’s average place to drop back (7)
24    Soundness of ship oddly slow across Channel (6)
25    Slat from special row (6)
27    Logical method has instrument working...