unrelenting
adj.continuing without stopping or slowing down. You use this to describe something that is very strong and hard to deal with.
adj.continuing without pause or cessation; relentless in intensity or force.
“The unrelenting rain made the hike very difficult.”
“Despite the unrelenting pressure from the board, the CEO refused to change his mind about the merger.”
“The unrelenting pace of the city's expansion eventually overwhelmed the local infrastructure, leading to a series of major traffic and water supply crises.”
“Mayor of London Sir Sadiq Khan is among those who have said Arday was subjected to unrelenting media scrutiny.”
“The Ministry of Manners’ laws demand constant, unrelenting politeness – no problem for Alfie, but his sister Margot is an outspoken firebrand.”
From un- + relenting.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.