The most common and most likely answer to this crossword clue is the 5 letter word STEAM
I've seen this crossword clue in The Times
S
T
E
A
M
More clues leading to the result STEAM
- Son heading side showing energy
- Cook leaves handwritten text about sandwiches
- Power in second eleven, perhaps
- One way to cook casserole wife’s missed before noon
- Stop harnessing atomic energy
- Hot air from 19th choice of squad?
- Cook eats roast mutton for starter
- Small group shows energy
- Old-fashioned uncle accepting note
- Small group of animals combined power
Buddy explains!

The straight part
We know that "Cook" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cook = steam.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 STEAM mean?
STEAM noun- The vapor formed when water changes from liquid phase to gas phase.
- Pressurized water vapour used for heating, cooking, or to provide mechanical energy.
- Internal energy for motive power.
- Pent-up anger.
- A steam-powered vehicle.
- Travel by means of a steam-powered vehicle.
- Any exhalation.
- Fencing without the use of any electric equipment.
- To cook with steam.
- To expose to the action of steam; to apply steam to for softening, dressing, or preparing.
- To produce or vent steam.
- To rise in vapour; to issue, or pass off, as vapour.
- To become angry; to fume; to be incensed.
- To make angry.
- To be covered with condensed water vapor.
- To travel by means of steam power.
- To move with great or excessive purposefulness.
- To exhale.
- Old-fashioned; from before the digital age.