Nigh means near, in old or poetic use. The end is nigh, nigh on impossible, draw nigh.
It survives in the end is nigh and in nigh on, meaning nearly — nigh on twenty years. It is the ancestor of near and next: near was originally its comparative and next its superlative, so the three are one word in three degrees. Note the silent gh.
1adverbnighNear.
“As night drew nigh, the travellers looked for somewhere to shelter.”
nigh is a measure of nearness.
NIGH → the NIGHt is near
The night is coming and it is nearly here now: not far off any more, but close enough to feel on your face.
hooks ontonight
Middle English
neygh
English, today
nigh
From Middle English neygh.
Etymology from Wiktionary, CC BY-SA