A
Cubit
is,
...the length of a man's arm from the elbow to the extremity of the middle finger.  The cubit among the ancients was of a different length among different nations.  Dr. Arbuthnot states the
Roman cubit at 17 inches and four tenths;
the cubit of the scriptures at a little
less than 22 inches; and the
English cubit at
18 inches.

Webster's  
1828   
Which of you by taking thought
can add one cubit unto his stature?
And why take ye thought for raiment?
Consider the lilies of the field, how they grow;
they toil not, neither do they spin:
And yet I say unto you,
That even Solomon in all his glory was
not arrayed like one of these.

Matthew 6:27-29