The most common and most likely answer to this crossword clue is the 13 letter word UNPUTDOWNABLE
I've seen this crossword clue in The Guardian
U
N
P
U
T
D
O
W
N
A
B
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E
More clues leading to the result UNPUTDOWNABLE
Buddy explains!
The straight part
We know that "like 16 across, if absorbing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case like 16 across, if absorbing = unputdownable.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 UNPUTDOWNABLE mean?
UNPUTDOWNABLE adjective- Of a person, etc.: difficult or impossible to put down (in various senses).
- (specifically) Of a book or other written work: so captivating or engrossing that one cannot bear to stop reading it.