The phrase "a formidable sum" is correct and usable in written English.
It can be used when referring to a large amount of money or a significant quantity of something that is impressive or intimidating.
Example: "The charity received a formidable sum in donations, allowing them to expand their outreach programs significantly."
Alternatives: "a substantial amount" or "a considerable sum."
Mr. Juck lost 25 of Montenapo's original 60 employees, and a formidable sum of money he declined to reveal.
He has pledged to spend millions by the primary election in September — not at Mr. Bloomberg's level, but still a formidable sum against opponents who, lacking personal fortunes, have agreed to abide by spending limits in exchange for public matching funds.
Still, this week Zopp's campaign leaked that it had already raised $665,000, a formidable sum.
Other countries including China, India, Israel, France and Pakistan are expected to devote formidable sums on tactical and strategic missile systems.
They also wonder if any change can provide enough resources to enable candidates to compete with those who can raise formidable sums without federal help.
The complex of policies that pushed the Philippines into the economic quagmire over the last 30 years can be summed up by a formidable term: structural adjustment.
Join a formidable network in Seoul.
While the sum total of the translation of the Zuck/Sandberg interview is a formidable beast of text, it's definitely worth the read.
As far as summing up the conference, this is of course a formidable task, because so much ground has been covered.
These interactions can take on a formidable diversity (Fig. 1a), generating complex patterns of mutual dependence among animals and plants that are more than the sum of the pairwise interactions.
In sum, performance-based pay is worth considering in some contexts; but making it work well and sustainably is a formidable challenge (OECD [2012]; Rowland and Potemski [2009]).
