The rumours will do untold damage to his reputation.untoldun‧told /ˌʌnˈtəʊld◂ $ -ˈtoʊld◂/ adjective [only before noun] 
The rumours will do untold damage to his reputation. The floods have caused untold misery to hundreds of homeowners.2used to emphasize that an amount or quantity is very largeuntold riches/wealth a game that offers untold wealth to the most talented players
EXAMPLES FROM OTHER DICTIONARIES
- Untold numbers of innocent people died in the prisons.
- It gobbled up still untold millions of dollars.
- Outside stood untold thousands of protesters and 10,000 state troops to quell them.
- Shaw had been brought up in untold luxury and was used to having his own money.
- There would be untold anguish to purge in the group sessions.
- They spent untold quantities of blood in pursuit of an inhuman ideology, with no compunctions and no second thoughts.
COLLOCATIONS FROM THE ENTRY The rumours will do untold damage to his reputation. The floods have caused untold misery to hundreds of homeowners. a game that offers untold wealth to the most talented playersCOLLOCATIONS FROM OTHER ENTRIES
1used to emphasize how bad something is: The rumours will do untold damage to his reputation. The floods have caused untold misery to hundreds of homeowners. a game that offers untold wealth to the most talented players (=so much harm that it cannot be described completely)· This type of abuse can cause a child untold harm.
COLLOCATIONS FROM THE CORPUSNOUN· However, incorrect stretching can cause untold damage and even permanent injuries in extreme cases.· Inaccurate information from an uninformed physician can cause untold damage to the best educational program.· They were already well within the shield zone and, had the barge been hostile, it could have inflicted untold damage.· The slide seemed empty, yet its contents could do untold damage.· On the contrary, said the voice, it could do his case untold damage.· It could inflict untold damage if he were to break that trust and be indiscreet.
· That had led to the war, and to untold misery before that, for several generations.· It's a familiar scene that can cause workers untold misery and loss of self-confidence.· Its regime - which Prince Philip believed would turn his sons into real men - had caused Charles untold misery and damage.
The rumours will do untold damage to his reputation. The floods have caused untold misery to hundreds of homeowners.2used to emphasize that an amount or quantity is very largeuntold riches/wealth a game that offers untold wealth to the most talented players