The most common and most likely answer to this crossword clue is the 8 letter word ENERGISE
I've seen this crossword clue in The Guardian
E
N
E
R
G
I
S
E
More clues leading to the result ENERGISE
- Motivate last pair of men before besieging foreign fighters
- Add zip to green pants in special exhibit initially
- Motivate men heading off before capturing US soldiers
- Green salad is primarily eaten to invigorate
- Stimulate singer to perform in centre of Queens
- Motivate English singer to perform Glyndebourne’s finale
- Nurse to show soldiers tablet to arouse
- Invigorate loco engineers with no end of passion
- Perk up, as one reneges, sadly
- Motivate soldier in deceptively serene setting
Buddy explains!

The straight part
We know that "Invigorate" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case invigorate = energise.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 ENERGISE mean?
ENERGISE verb- To invigorate; to make energetic.
- To supply with energy, especially electricity; to turn on power to (something).
- To use strength in action; to act or operate with force or vigor; to act in producing an effect.