The most common and most likely answer to this crossword clue is the 7 letter word HEFTIER
I've seen this crossword clue in Financial Times
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More clues leading to the result HEFTIER
Buddy explains!

The straight part
We know that "weightier" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case weightier = heftier.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 HEFTIER mean?
HEFTIER adjective- Heavy, strong, vigorous, mighty, impressive.
- Strong; bulky.
- (of a person) Possessing physical strength and weight; rugged and powerful; powerfully or heavily built.
- Heavy, weighing a lot.
- (of a number or amount) Large.