The most common and most likely answer to this crossword clue is the 6 letter word TRYING
I've seen this crossword clue in Financial Times
T
R
Y
I
N
G
More clues leading to the result TRYING
- Hard, but having a go
- Difficult time with Yankee in boxing venue
- Judging is exasperating
- Hard - of hearing?
- Tiresome Yankee visiting Herts town
- Selection of poetry in Greek requiring effort
- Hearing test in building at the end
- Judge’s job is tedious
- Difficult linking rings really, at first
- Tiresome scribbler finally stops drawing
Buddy explains!

The straight part
We know that "Tiresome" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case tiresome = trying.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 TRYING mean?
TRYING verb- To attempt; to endeavour. Followed by infinitive.
- To divide; to separate.
- To test, to work out.
- To experiment, to strive.
- To lie to in heavy weather under just sufficient sail to head into the wind.
- To strain; to subject to excessive tests.
- (used with another verb) To want
- The act by which one tries something; an attempt.
- Difficult to endure; arduous.
- Irritating, stressful or bothersome.