Latin longus < *dlh1-ongh-o

Hello,

I saw some difficulties to link Latin & Germanic 'long' to the root
for long: *delh1gh-o ; *dolh1gh-o ; *dlh1gh-o

The idea that I have seen is to consider the root to be only *delh1-

like: *delh1-gh-o ; *dolh1-gh-o ; *dlh1-gh-o

and in this case Latin & Germanic 'long' are derived as:

PIE *dlh1-ongh-o > [dl>l] > Latin longus

NOTE: however the lost of initial d seems to date to a Dialectal IE
period based on Germanic 'long' too (see also Lithuanian ilgas < *(d)
lh1gh-o)


My questions are:
1. what is the meaning of the root *delh1- in this case?
2. what is the meaning of the extension -gh- ? Do we have similar
constructions?

Thanks in advance,
Marius