The most common and most likely answer to this crossword clue is the 4 letter word BULL
I've seen this crossword clue in The Daily Telegraph
B
U
L
L
More clues leading to the result BULL
- Back off cow or its mate
- Male whale? Nonsense
- One seeing what’s going to be charged for sweet
- Earthmovers removing sleepers and rubbish
- Stupid speculator was first in
- Nonsense … it’s worth fifty!
- Central target, male on the field?
- Good shot brings oppressor to premature end
- Person who’s investing gold in 17?
- Speculator and powerful man
Buddy explains!

The straight part
We know that "Lower/middle" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case lower/middle = bull.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 BULL mean?
BULL noun- An adult male of domesticated cattle or oxen.
- A male of domesticated cattle or oxen of any age.
- Any adult male bovine.
- An adult male of certain large mammals, such as whales, elephants, camels and seals.
- A large, strong man.
- An investor who buys (commodities or securities) in anticipation of a rise in prices.
- A policeman.
- A crown coin; its value, 5 shillings.
- (Philadelphia) A man.
- A man who has sex with another man's wife or girlfriend with the consent of both.
- A drink made by pouring water into a cask that previously held liquor.
- Large and strong, like a bull.
- (of large mammals) adult male
- Of a market in which prices are rising (compare bear)
- Stupid
- The centre of a target, inside the inner and magpie.
- A shot which hits the centre of a target.
- The two central rings on a dartboard.
- A hard striped peppermint-flavoured boiled sweet.
- Thick glass set into the side of a ship to let in light.
- A hand-cancelled postmark issued by a counter clerk at a post office, typically done on a receipt for proof of mailing.
- The central part of a crown glass disk, with concentric ripple effect.
- A convex glass lens which is placed in front of a lamp to concentrate the light so as to make it more conspicuous as a signal; also the lantern itself.
- A £50 banknote.
- Any of the first postage stamps produced in Brazil from 1843.
- The faeces of a bull.
- False or exaggerated statements made to impress and deceive the listener rather than inform; nonsense.
- A card game in which the object is to bluff about cards laid down and to determine when one's opponents are bluffing.
- An object of frustration and/or disgust, often caused by a perceived deception.
- Statements that may be true but misleading nonetheless.
- Statements made without any particular reference to their truth value.
- To force oneself (in a particular direction).
- To lie, to tell untruths.
- To be in heat; to manifest sexual desire as cows do.
- To polish boots to a high shine.
- To endeavour to raise the market price of.
- To endeavour to raise prices in.
- A papal bull, an official document or edict from the Pope.
- A seal affixed to a document, especially a document from the Pope.
- (17th century) to publish in a Papal bull
- A lie.
- Nonsense.
- To mock; to cheat.
- (16th century) A bubble.