The most common and most likely answer to this crossword clue is the 5 letter word OOMPH
I've seen this crossword clue in The Times
O
O
M
P
H
More clues leading to the result OOMPH
- Energy old politician displayed in backing House
- It is over the rate of being still
- Go round twice at speed
- Vitality of the sound of low brass out of key
- Ginger loves the going rate
- Drive round with zero speed
- Nothing old having speed and energy
- Go round and round at speed
- Balls: politician with hot sex-appeal!
- Ginger gets glasses at the going rate
Buddy explains!

The straight part
We know that "Go" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case go = oomph.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 OOMPH mean?
OOMPH noun- Strength, power, passion or effectiveness; clout.
- Sex appeal.
- A bassy grunting or thudding sound.
- To produce a bassy grunting or thudding sound.