- 1901 oozed
- 1902 oozes
- 1903 oozier
- 1904 ooziest
- 1905 oozily
- 1906 ooziness
- 1907 oozing
- 1908 oozy
- 1909 op
- 1910 opacified
- 1911 opacifier
- 1912 opacifies
- 1913 opacify
- 1914 opacifying
- 1915 opacities
- 1916 opacity
- 1917 opacous
- 1918 opah
- 1919 opal
- 1920 opaled
- 1921 opalesce
- 1922 opalesced
- 1923 opalescence
- 1924 opalescent
- 1925 opalescently
- 1926 opalesces
- 1927 opalescing
- 1928 opaleye
- 1929 opaline
- 1930 opalised
- 1931 opalized
- 1932 opals
- 1933 opaque
- 1934 opaqued
- 1935 opaquely
- 1936 opaqueness
- 1937 opaquer
- 1938 opaques
- 1939 opaquest
- 1940 opaquing
- 1941 opcode
- 1942 ope
- 1943 opec
- 1944 oped
- 1945 opeidoscope
- 1946 opel
- 1947 open
- 1948 openabilities
- 1949 openability
- 1950 openable
- 1951 openair
- 1952 opencast
- 1953 opened
- 1954 openedup
- 1955 opener
- 1956 openers
- 1957 openest
- 1958 openhanded
- 1959 openhandedly
- 1960 openhandedness
- 1961 openhearted
- 1962 openheartedly
- 1963 openheartedness
- 1964 openhouse
- 1965 opening
- 1966 openings
- 1967 openly
- 1968 openminded
- 1969 openmindedness
- 1970 openmouthed
- 1971 openmouthedly
- 1972 openmouthedness
- 1973 openness
- 1974 openout
- 1975 opens
- 1976 openwork
- 1977 opepe
- 1978 opera
- 1979 operabilities
- 1980 operability
- 1981 operable
- 1982 operably
- 1983 operagoer
- 1984 operagoing
- 1985 operand
- 1986 operant
- 1987 operantly
- 1988 operants
- 1989 operas
- 1990 operaschool
- 1991 operate
- 1992 operated
- 1993 operates
- 1994 operatic
- 1995 operatically
- 1996 operatics
- 1997 operating
- 1998 operation
- 1999 operational
- 2000 operationalism