Adventurers seeing 1,000 things, conceivably (7,6)

'adventurers' is the definition.
Both the answer and definition are plural nouns.
Maybe there's a link between them I don't understand?

'1000 things conceivably' is the wordplay.
I cannot really understand how this works, but
'1000' could be 'k' (synonyms) and 'k' is found in the answer.
an anagram of 'things' is 'nights' which is within the answer.
The remaining letters 'errant' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

'seeing' is the link.

Can you help me to learn more?