Be lumbered with harvesting at first by more senior squire (4-6)

'squire' is the definition.
Both the answer and definition are singular nouns.
Maybe you can see an association between them that I don't see?

'be lumbered with harvesting at first by more senior' is the wordplay.
'be lumbered with' becomes 'land' (I can't justify this - if you can you should believe this answer much more).
'at first' suggests taking the first letters.
'by' says to put letters next to each other.
'more senior' becomes 'older' ('old' can be similar in meaning to 'senior').
The first letter of 'harvesting' is 'h'.
'land'+'h'+'older'='LAND-HOLDER'

Can you help me to learn more?