Sailor, soldier and university lecturer start to attack spider (9)
I believe the answer is:
tarantula
'spider' is the definition.
(tarantula is a kind of spider)
'sailor soldier and university lecturer start to attack' is the wordplay.
'sailor' becomes 'tar' (tar is a kind of sailor).
'soldier' becomes 'ant' (I've seen this before).
'and' says to put letters next to each other.
'university lecturer' becomes 'ul' (this might be a standard abbreviation I've not previously seen).
'start to' suggests taking the first letters.
The initial letter of 'attack' is 'a'.
'tar'+'ant'+'ul'+'a'='TARANTULA'
(Other definitions for tarantula that I've seen before include "Large venomous spider" , "small, venomous creature" , "A big hairy spider" , "Leggy creature" , "web developer" .)