1. (adjective) not to be placated or appeased or moved by entreaty

• grim
• inexorable
• relentless
• stern
• unappeasable
• unforgiving

2. (adjective) harsh

• brutal

3. (adjective) never-ceasing

• persistent
• relentless

1. (adjective) not to be placated or appeased or moved by entreaty

• implacable

2. (adjective) harsh

• intense

3. (adjective) never-ceasing

• continual

1. (adjective) not to be placated or appeased or moved by entreaty

• asperity
• grimness
• hardship
• rigor
• rigorousness
• rigour
• rigourousness
• severeness
• severity
• inexorability
• inexorability
• inexorability
• inexorableness
• inexorableness
• inexorableness
• relentlessness
• relentlessness
• relentlessness
• sternness
• strictness

2. (adjective) never-ceasing

• continuity
• persistence
• doggedness
• perseverance
• persistence
• persistency
• pertinacity
• tenaciousness
• tenacity
• hang in
• hang on
• hold on
• persevere
• persist
• inexorability
• inexorableness
• relentlessness