Domain Name

I am madly, deeply in love with this comment LoL.

Ok, so, domain name...
Yep, make sure keywords in domain name. I wrote something much longer, but commonly, the competitive keywords are likely taken in a single-word singleword.com variant. So, you want to find variants on this instead of paying singleword.com's owner thousands of bucks.

So, adjectives or common nouns that are commonly searched alongside the keyword are a good start to finding alternatives. (best, better, find, review, search)
singlewordadjective.com
adjectivesingleword.com

Adding a "stop" word (the, a, and (etc))
asingleword.com
thesingleword.com

Combining the above 2 strategies can be mildly effective when absolutely required.

For a 2-word phrase
(twoword.com, or firstsecond.com) is typically preferred.

if not:
hyphens are good alternative
two-word.com or first-second.com

if not, then:
using/spinning above variations (adjectives/verbs/"stop" words)

if not, then:
combine hyphens WITH these methods.

Worst case scenario with this or a similar strategy would result in something like:

singleword-noun.com (keyword-review.com, best-keyword.com, etc) which IMO atleast reads better than 123keyword4u.com (OMG I've seen some WINNERS LOL!!!)

And if none of the above seem to cut it for you:
pay singleword.com's owner thousands of bucks or come up with a different niche.

Good luck.
-Kevin