Synonym: cruel, firm, hard, harsh, heartless, inflexible, merciless, persevering, persistent, rigid, ruthless, steadfast, strict, uncompromising, unsympathetic, unyielding. Similar words: talentless, gentleness, pointless, careless, relent, unrelentingly, tactlessness, witless. Meaning: [rɪ'lentlɪs] 
adj. 1. not to be placated or appeased or moved by entreaty 2. never-ceasing.
adj. 1. not to be placated or appeased or moved by entreaty 2. never-ceasing. 
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151. How do we know this relentless one-upmanship is a biological endowment?
152. Prime Minister Vladimir Putin, a KGB veteran, has concertedly molded the SVR in the image of its Soviet-era predecessor, most of all in its relentless focus on spying on the West.
153. She says these experts have highly-developed powers of observation, and a relentless motivation and commitment to uncovering the truth.
154. Long abandoned by a broken-down bus, my team and I were forced to climb a mountain under the relentless sun.
155. He was the most relentless enemy I have ever known.
156. The Islamic Republic of Iran is a true revolutionary power. Its central theme has been its relentless attacks, in words and deeds,(sentence dictionary) on the international system.
157. This early join of life and death continues to impel his relentless pursuit of cinematic invention.
158. The pernickety, timeless , relentless nature of the accession process is the whole point.
159. It wasn't just the struggles of these men and women that had moved me. Rather, it was their determination, their self-reliance, a relentless optimism in the face of hardship.
160. Additionally, in the lead-up to the bombing, the family were under relentless scrutiny from law enforcement agencies.
161. Relentless and indefatigable in pursuit or as if in pursuit.
162. That changed when Qaddafi's forces came at them with relentless force, driving them, helter-skelter, into retreat.
More similar words: talentless, gentleness, pointless, careless, relent, unrelentingly, tactlessness, witless, tactless, useless, tactlessly, nonetheless, homeless, hopeless, silently, tasteless, guileless, senseless, violently, changeless, insolently, nevertheless, malevolently, mantle, helen, at length, subtitles, release, reluctantly, nettlesome.