Provocation on steamship is not desired (8)
I believe the answer is:
needless
'not desired' is the definition.
The answer and definition are not the same part of speech. However, past participle verbs and adjectives can sometimes define each other.
'provocation on steamship' is the wordplay.
'provocation' becomes 'needle' (needle can mean to provoke or annoy).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'steamship' becomes 'ss' (nautical abbreviation).
'needle'+'ss'='NEEDLESS'
'is' is the link.
Can you help me to learn more?
(Other definitions for needless that I've seen before include "luxury" , "Otiose" , "Lessened, being without good cause" , "Superfluous" , "without provocation?" .)