The most common and most likely answer to this crossword clue is the 5 letter word SNIFF
I've seen this crossword clue in The Daily Telegraph
S
N
I
F
F
More clues leading to the result SNIFF
Buddy explains!

The straight part
We know that "smell" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case smell = sniff.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 SNIFF mean?
SNIFF noun- An instance of sniffing.
- A quantity of something that is inhaled through the nose
- A brief perception, or tiny amount.
- Cocaine.
- To make a short, audible inhalation, through the nose, as when smelling something.
- To say something while sniffing, for example in case of illness or unhappiness, or in contempt.
- To perceive vaguely
- To be dismissive or contemptuous of something.
- To intercept and analyse packets of data being transmitted over a network.
- To inhale drugs in powder form (usually cocaine) through the nose.
- A short inhalation sound, sometimes associated with crying.