Significant amounts made on raids at sea (7)
I believe the answer is:
inroads
'significant amounts' is the definition.
Although both the answer and definition are plural nouns, I cannot understand how they can define each other.
'on raids at sea' is the wordplay.
'at sea' is an anagram indicator.
'on'+'raids'='onraids'
'onraids' is an anagram of 'INROADS'.
'made' is the link.
Can you help me to learn more?
(Other definitions for inroads that I've seen before include "Sad iron (anag.)" , "(Make) raids, intrusions (into)" , "Encroachments" , "Progress" , "large quantities consumed when these are made" .)