The most common and most likely answer to this crossword clue is the 5 letter word OTTER
O
T
T
E
R
More clues leading to the result OTTER
- Excessive sign of hesitation in river creature
- Boy wizard would have power over this aquatic creature
- Fur making cockney thus?
- Swimmer's more fashionable without a top
- Cruel person beheaded river creature
- Swimmer finished poetically, clinching races
- Creature that swims from pilot, terrified
- Good swimmer, going too far, about to flip
- Cruel person’s beheaded river mammal
- Heading off rat, aquatic animal
Buddy explains!

The straight part
We know that "mammal" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case mammal = otter.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 OTTER mean?
OTTER noun- An aquatic or marine carnivorous mammal in the subfamily Lutrinae of the family Mustelidae, which also includes weasels, polecats, badgers, and others.
- A hairy man with a slender physique, in contrast with a bear, who is more thickset.
- Annatto (dye)