suffering: a specific affliction or hardship that a person undergoes
At its core this word names something you undergo rather than something you do. It is built on the ordinary Greek verb meaning "to suffer," and it points to a particular hardship experienced, a single affliction endured, rather than a general mood or state. That sets it a little apart from a closely related noun (πάθος), which names the inner condition of being stirred up; this word names the concrete thing suffered.
Outside the Bible the word ranged very widely, covering everything from public calamities to bodily symptoms. The New Testament writers narrow it almost entirely to human suffering, and above all to "the sufferings of Christ." That phrase became a near-fixed expression that ties the suffering Jesus endured to the ongoing suffering of his followers, who are said to share in it.
So the meaning splits into two shades. Sometimes it is plain human hardship: persecution, distress, the troubles of the present age. Other times it is the loaded, Christ-centered sense, where a believer's suffering is drawn into the pattern of Jesus' own. Scholars line up the same set of occurrences and agree on the wording; where they differ is on how deeply the believer really participates in Christ's suffering, which is a question of theology rather than of what the word means. Note too that this is a different word from another common term for hardship (θλῖψις), which pictures affliction as outward pressure.