Philistine always knocked over? Goliath finally ducks (5)
I believe the answer is:
yahoo
'philistine' is the definition.
(thesaurus)
'always knocked over? goliath finally ducks' is the wordplay.
'always' becomes 'ay'.
'knocked over?' is a reversal indicator (I've seen 'knock over' mean this).
'finally' suggests the final letters.
'ducks' becomes 'oo' (I've seen this in other clues).
The final letter of 'goliath' is 'h'.
'ay' written backwards gives 'ya'.
'ya'+'h'+'oo'='YAHOO'
(Other definitions for yahoo that I've seen before include "Uncivilised brute(Swift)" , "shout of joy" , "Race of brutes in Gulliver's Travels" , "Human-looking beast in Gulliver's Travels: search engine conglomerate" , "One of Dean Swift's brute people" .)