The most common and most likely answer to this crossword clue is the 4 letter word FUSE
F
U
S
E
More clues leading to the result FUSE
- Female exploitation displayed by Bond
- Join together in fine employment
- Factory’s first exercise to produce safety device
- Rubbish mostly run together
- Safety device from America with iron casing
- Safety device that may be installed in a bomb
- Melt together — put out the lights!
- Combine force and exercise
- Join American in Florence on vacation
- Heard expressions of relief from circuit breaker
Buddy explains!

The straight part
We know that "Join" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case join = fuse.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 FUSE mean?
FUSE noun- A cord that, when lit, conveys the fire to some explosive device.
- The mechanism that ignites the charge in an explosive device.
- A device to prevent the overloading of an electrical circuit, containing a component that melts and interrupts the current when too high a load is passed through it.
- Indicating a tendency to lose one's temper.
- A friction match for smokers' use, having a bulbous head which when ignited is not easily blown out even in a gale of wind.
- A kind of match made of paper impregnated with niter and having the usual igniting tip.
- To melt together; to blend; to mix indistinguishably.
- To melt together.
- To furnish with or install a fuse.
- To form a bicyclic compound from two similar or different types of ring such that two or more atoms are shared between the resulting rings