ADJ

excellent, fertile, good, lucrative, reliable, rich, valuable
a fertile source of ideas a lucrative source of income a rich source of vitamins
important, main, major, principal
cheap
a cheap source of labour
external, foreign
Do you have any foreign sources of income?
independent
an independent source of funding
additional
alternative
We need to look for alternative sources of energy
natural
renewable
The village obtains all its energy from renewable sources
energy, food, heat, light, power, water

VERB + SOURCE

be, constitute, prove, provide
The census constitutes the principal source of official statistics. These crustaceans provide a valuable food source for some fish
exploit, tap, use (as)
The government hopes to tap new sources of employment in the area of health
locate
We tried to locate the source of the sound

PREP

at ~
Under the PAYE system, employees' income is taxed at source (= by the employer)
~ of
a reliable source of advice

PHRASES

a variety of sources
The research was funded from a wide variety of sources

ADJ

invaluable, useful, valuable
authoritative, informed, reliable, reputable
unreliable
original
independent
anonymous
primary, secondary
published
biographical, documentary, historical, literary, written
diplomatic, government, intelligence, military, official, police
Intelligence sources report a build-up of troops just inside the border
data, information

VERB + SOURCE

use (as)
cite, quote
Researchers try to quote primary sources wherever possible
disclose, name, reveal
The police refused to reveal the source of their information

SOURCE + VERB

claim sth, describe sth, disclose sth, indicate sth, report sth, reveal sth, say sth, suggest sth
Government sources indicated that a compromise might be reached. One source said: 'Our blood is up. We are angry at the way we have been treated.'
deny sth

SOURCE + NOUN

material

PREP

according to ~s
According to informed sources, a takeover bid is planned for next month
~ of

PHRASES

sources close to sb
Sources close to the player claim he won't be entering this year's championship