The most common and most likely answer to this crossword clue is the 4 letter word KNOB
K
N
O
B
Buddy explains!
The straight part
We know that "lump" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case lump = knob.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does KNOB mean?
KNOB noun- A rounded protuberance, especially one arising from a flat surface; a fleshy lump or caruncle.
- A rounded control switch that can be turned on its axis, designed to be operated by the fingers.
- A ball-shaped part of a handle, lever, etc., designed to be grabbed by the hand.
- A rounded ornament on the hilt of an edged weapon; a pommel.
- A prominent, rounded bump along a mountain ridge.
- A prominent rounded hill.
- (chiefly in the plural) A woman's breast.
- The penis.
- The head of the penis; the glans.
- (by analogy with above) A contemptible person.
- A dollop, an amount just larger than a spoonful (usually referring to butter).
- A chunky branch-like piece, especially of a ginger rhizome.
- A bulb of the garlic plant consisting of multiple cloves.
- (of a man) To have sex with.